Copper (Cu) elimination was investigated in the tissue and organs of rainbow trout (Oncorhynchus mykiss, Walbaum, 1792), after Cu-free diets exposure. In the current study, fish were fed to satiation on diets containing 0.022 (Group 1; Control), 0.043 (Group 2), 0.123 (Group 3), 0.424 (Group 4) g Cu*kg -1 diet for 60 days before elimination experiment. A total of 288 fish (mean weight 84.28±1.05 g) were randomly transferred to 12 fibreglass tanks. The fish were fed the Cu-free diet twice daily, until apparent satiation, during 60 days. Subsequently, the experiment was established for a period of elimination, during which samples were taken at days 15, 30, 45 and 60. Cu concentration in the muscle, gill tissue, digestive system, liver and whole body of fish were determined after 60 days depuration.Cu concentrations in tissues of rainbow trout decreased during depuration period, and the order of Cu elimination in tissue and organs of rainbow trout was: digestive system (73.1 %), then gill (41.1 %), muscle (31.5 %) and liver (17.2 %) for group 2; digestive system (74.1%), then muscle (65.8%), gill (60.0%) and liver (34.6%) for group 3; and digestive system (85.8%), then muscle (80.8%), liver (50.5%) and less/equal in gill (50.2%) for group 4. In statistical analysis, both groups and time were significant factors (P<0.05) on elimination rate. Moreover, significant interaction between groups and time were identified on elimination rate. Digestive system showed the fastest elimination rates of Cu at all groups compared with other tissues.

A feeding trial of 84 days was carried out to evaluate the effects of olive cake (OC) on growth, feed utilization, digestibility of nutrient, haematological values and some blood chemistry parameters of juvenile hybrid tilapia (Oreochromis niloticus × Oreochromis aereus). Four diets were prepared including OC at levels of 0, 120, 240 and 360 g kg−1. Twenty fish per tank (initial weight 8.58 ± 0.09 g) were randomly distributed into 200‐L fibreglass tanks. Final body weight and specific growth rate of fish fed with diets OC12 were not significantly different compared to fish fed with the control diet. The best feed conversion rate and protein efficiency rate were obtained from the fish fed with the control and OC12 diets. Growth performance, feed conversion rate and protein efficiency rate of fish fed diets with OC incorporation levels of more than 12 per cent tended to decrease significantly (P < 0.05) compared to the control and OC12 diet groups. The apparent digestibility coefficients (ADC) of dry matter significantly decreased (P < 0.05) with the increase of dietary OC levels, whereas the ADC of protein was not affected by dietary treatment. The ADC of lipid of fish fed with control and OC12 diets were significantly (P < 0.05) higher than those of fish fed with OC24 and OC36 diets. Mean corpuscular haemoglobin, cholesterol and triglycerides were affected by dietary OC level. The findings of this study show that OC can be incorporated to diets of juvenile hybrid tilapia up to 120 g kg−1 without any adverse effect on fish growth and feed utilization.

No abstract